1. Technical Field
The present disclosure relates to a variable nozzle unit capable of varying the area of a passage (a flow rate) of an exhaust gas to be supplied to a turbine impeller in a variable geometry system turbocharger, and the like.
2. Description of the Related Art
Various developments have been made for a variable nozzle unit to be placed inside a turbine housing of a variable geometry system turbocharger. The applicant of this application has already filed applications related to developments for the variable nozzle unit (see Japanese Patent Application Laid-Open Publication Nos. 2009-243431 (PTL1), and 2009-243300 (PTL2)). A configuration of the variable nozzle unit related to the conventional technique is as follows.
A support ring is placed inside a turbine housing. The support ring includes an annular base portion. A cylindrical intermediate portion is formed on an outer peripheral edge of this base portion (the base portion of the support ring) to project toward one side in an axial direction of a turbine impeller. Furthermore, an annular tip end edge portion (flange portion) is integrally formed on a tip end edge of the intermediate portion of the support ring to project outward in a radial direction of the support ring. The tip end edge portion (the flange portion of the support ring) is held between the turbine housing and a bearing housing of a variable geometry system turbocharger.
A nozzle ring is integrally provided to the base portion of the support ring by joining end portions (end portions in the axial direction) respectively of three or more connection pins to the base portion by riveting, where the connection pins are arranged in the circumferential direction of the support ring. At a position away from the nozzle ring in the axial direction, a shroud ring is integrally provided to the nozzle ring by fitting opposite end portions (opposite end portions in the axial direction) respectively of the multiple connection pins to the shroud ring (by riveting). The shroud ring covers tip end edges of multiple turbine blades of the turbine impeller.
Between mutually-facing surfaces of the nozzle ring and the shroud ring, multiple variable nozzles are placed at equal intervals in the circumferential direction. Each variable nozzle is turnable in forward and reverse directions (opening and closing directions) on its axis parallel with an axis of the turbine impeller. In this respect, when the multiple variable nozzles are synchronously turned in the forward direction (opening direction), the area of a passage of an exhaust gas to be supplied to the turbine impeller increases. When the multiple variable nozzles are synchronously turned in the reverse direction (closing direction), the area of the passage of the exhaust gas to be supplied to the turbine impeller decreases.